Microbial community analysis of three hydrocarbon reservoir cores provides valuable insights for the assessment of reservoir souring potential Nicolas Tsesmetzis a, * , Eric B. Alsop a, b , Adrien Vigneron a, c , Fons Marcelis d , Ian M. Head c , Bart P. Lomans d a Shell International Exploration and Production Inc., Houston, TX, USA b DOE Joint Genome Institute, Walnut Creek, CA, 94598, USA c School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK d Shell Global Solutions International B.V., Rijswijk, Netherlands article info Article history: Received 1 February 2016 Received in revised form 19 July 2016 Accepted 2 September 2016 Available online xxx Keywords: Reservoir core Microbial profile Reservoir souring Next generation sequencing Hydrocarbons Souring potential assessment abstract Three hydrocarbon reservoir cores were obtained from a high temperature non-waterflooded offshore reservoir. All three cores were taken from a 56-m section of the same well. Under sterile conditions, DNA was recovered from the inner section of each core and the microbial community profiles were deduced by sequencing the 16S rRNA marker gene. Taxonomic analysis of the Operational Taxonomic Units (OTUs) recovered, identified a high proportion of members from the Oxalobacteraceae family (38.5%) followed by members from the Pseudomonadaceae and Comamonadaceae families (29.1% and 12.8% respectively). Representatives of all these families are known to degrade hydrocarbons as well as to use nitrate as a terminal electron acceptor under anaerobic conditions. Assuming these predominant microorganisms are indigenous to the reservoir and have not been introduced with the drilling fluids they might exhibit a relatively rapid response to nitrate injection for souring control. On the contrary, very few sulfate reducing bacteria (SRBs) were detected in these cores (<0.01%) suggesting unfavorable conditions to SRB growth. This however may well rapidly change upon seawater injections in the absence of nitrate addition. This study sets the microbial profiling “baseline” for the prediction of souring through modelling as well as for any upcoming biomonitoring surveys. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Subseafloor sediments and deep subsurface biosphere eco- systems host a large number of microbial cells (2.9  10 29 cells) with a range of metabolic capabilities (D'Hondt et al., 2004; Kallmeyer et al., 2012). Although bacterial abundance decreases logarithmically with depth, active microbial communities have been detected down to 2500 m below the seafloor (Inagaki et al., 2015) and bacterial endospores have also been detected in deeply buried sediments (Lomstein et al., 2012). Temperature, which increases linearly along a gradient of 24  Ce36  C per kilometer of depth, is considered as one of the major limiting factors for life in subseafloor sediments. Temperatures close 100  C, found theo- retically around 3 km below the seafloor, normally denature proteins, membranes and nucleic acids, inhibiting most microbial life (Rothschild and Mancinelli, 2001). Furthermore, prolonged exposure to high temperature, also known as paleo- pasteurization, can limit microbial life in subsurface sediments (Adams et al., 2006). The availability of nutrients and degradable substrates is also a strong limiting factor for microbial growth and activity in subsurface environments (Head et al., 2003). However, within the large expanses of nutrient and substrate poor sedi- ments of the deep biosphere, oil reservoirs might be considered oases. Indeed, oil reservoirs harbor a large variety of hydrocarbon and/or gas deposits which can be degraded and used as carbon sources by microorganisms (Head et al., 2003). Furthermore, Abbreviations: MIC, microbially influenced corrosion; SRBs, sulfate reducing bacteria; NRBs, nitrate reducing bacteria. * Corresponding author. Shell Technology Centre Houston, 3333 Highway 6 South, Houston, 77082, TX, USA. E-mail address: nicolas.tsesmetzis@shell.com (N. Tsesmetzis). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod http://dx.doi.org/10.1016/j.ibiod.2016.09.002 0964-8305/© 2016 Elsevier Ltd. All rights reserved. International Biodeterioration & Biodegradation xxx (2016) 1e12 Please cite this article in press as: Tsesmetzis, N., et al., Microbial community analysis of three hydrocarbon reservoir cores provides valuable insights for the assessment of reservoir souring potential, International Biodeterioration & Biodegradation (2016), http://dx.doi.org/10.1016/ j.ibiod.2016.09.002